In the practical or successful operation of a ring laser type gyro, it is necessary to adjust the length of the laser optical path to achieve that optimum laser frequency associated with maximum laser gain. Also, adjustment of the alignment of the laser optics is required for stabilizing system losses.
In other words, an optimum path length adjustment is sought for maximum laser intensity, while maintenance of an optimum optical path alignment is sought in order to maintain optical cavity losses preferrably at a minimum or at least at a constant value. Thus, by means of both adjustments, a peak laser output intensity is obtained and gyro bias stabilization is improved.
Prior methods for effecting such adjustments have relied upon movable mirrors for path length adjustment and stable geometry of mechanically positioned optical elements. However, obvious limits are imposed with regard to the mechanical tolerances and geometric stability achievable for a given design and choice of materials. Also, such limits are approached only at high unit costs and manufacturing expense. Further, the error sources associated with such limits are subject to change due to thermal expansion, material "creep" and the like.
Laser gyro path length control has been effected by control of a movable mirror interposed in the laser optical path. In such prior art arrangement, the path length is modulated to produce a modulated beam intensity which may be photoelectrically sensed and synchronously demodulated to provide an error path signal for closed loop control of the movable mirror. However, such control mode mechanization serves no other control mode function, such as optical path alignment.